NFL sacks champion Robert Mathis admits he made a mistake late last season.

Now it's going to cost him -- four games and four paychecks.

The Colts' career sacks leader was suspended Friday by the NFL after violating the league's ban on performance-enhancing substances. What exactly Mathis tested positive for remains a mystery but the linebacker said in a statement he was seeking fertility assistance. He acknowledged that he and his wife are expecting a baby.

"I am deeply saddened that this situation will prevent me from contributing to my team for four games, and I regret that I didn't cross check what my doctor told me before I took the medication, " Mathis said. "I hope that my fans will understand the unique circumstances involved here and continue to know that I am a man of integrity who would never intentionally circumvent the performance enhancing substance policy agreed to by the NFL and my union."

Mathis said Commissioner Roger Goodell denied Mathis' request to not issue a suspension based on the circumstances.

The league issued a statement Friday night about the case:

"As Mr. Mathis's agent acknowledged today, his client failed to follow the protocols in the policy that the NFL and NFLPA agreed upon to address precisely these kinds of claims," the NFL said. "That policy also prescribes the disciplinary consequences of a positive test. The policy does not provide - nor should it provide - for the commissioner to override the policy's procedures and assess discipline on an after-the-fact, ad hoc basis. Here Mr. Mathis actually withdrew his appeal and accepted discipline at the union's suggestion. His hearing took place only after the Players Association requested that the appeal be reinstated.

FOX SPORTS DAILY

NFL TEAM EDITION

NFL News To Your Inbox!

"The drug for which Mr. Mathis tested positive is not approved by the FDA for fertility in males and is a performance-enhancing drug that has been prohibited for years. Importantly, Mr. Mathis did not consult with the policy's independent administrator, a physician jointly approved by the NFL and NFL Players Association. Nor did he consult with his team doctor, the team's training staff, the NFLPA, the league office or the hotline established under the policy to give confidential information to players. Each of these sources would have warned against using this substance.

"A cornerstone of the program is that a player is responsible for what is in his body. Consistent application of the policy's procedures is critical to the integrity of the program."

If the NFL's decision stands, and they almost always do, Mathis would not be eligible to rejoin the Colts until Sept. 29. He is allowed to participate in the team's offseason workouts, training camp and preseason games.

The Colts quickly issued a statement saying they would support Mathis, one of the team's elder statesmen and most respected leaders. Mathis set a single-season record with 19 sacks last season and also broke Dwight Freeney's franchise career record for sacks. In 11 NFL seasons, Mathis has 111 career sacks.

"We nevertheless wish to assure Robert and our fans that he remains an honored and cherished member of the Colts family and that we support him as he deals with this difficult challenge," Mathis said.

It's another black eye for a franchise whose owner, Jim Irsay, was arrested near his suburban Indy home in March and preliminarily charged with four felony counts of possession of a controlled substance and a misdemeanor driving while intoxicated charge. Irsay sought medical help two days later and did not return to the team until last weekend's draft. Irsay has not spoken publicly about what happened.

Mathis was considered an undersized defensive end when the Colts took him in the fifth round of the 2003 draft.

It didn't take long, though, for Mathis and Freeney to form one of the NFL's most feared pass-rushing combinations.

With Mathis developing his own spin moves to match Freeney, and Freeney developing his own tomahawks chop, imitating Mathis, the two close friends not only put quarterbacks on the ground, they forced fumbles at the league's highest rate, too.

Both emerged as perennial Pro Bowlers, but when they were asked to move to linebacker in new coach Chuck Pagano's 3-4 defense, Mathis thrived and Freeney struggled.

When the Colts announced last year that they would not re-sign Freeney, many thought Mathis would struggle.

Instead, he had the best season of his career and became the first winner of the Deacon Jones Award. Defending that title might be next to impossible in 2014 -- unless he wins an appeal.

"We are thrilled that we will be welcoming a new (family) member in several months, but I apologize to my teammates, coaches and Colts fans that I will not be able to contribute to my team for the first four weeks of the 2014 season," Mathis said. "I will work extremely hard during that time to stay in top football shape and will be prepared to contribute immediately upon my return."